1. Field of the Invention
This invention relates to an exhaust gas apparatus and a method for purifying an exhaust gas in an internal combustion engine.
2. Related Art of the Invention
There is known an apparatus for purifying an exhaust gas disclosed in a Japanese Issue Patent Publication No. 2722987. The earlier technology includes a diesel particulate filter (DPF) and a NOx trap catalyst disposed in an exhaust passage wherein the DPF traps particulate matters (PM) in an exhaust gas and the NOx trap catalyst traps NOx in the exhaust gas flowing when an air-fuel ratio in the exhaust gas is in a lean range and purifies the trapped NOx when the air-fuel ratio is in a rich range. The particulate matters deposited in the DPF and the NOx deposited in the NOx trap catalyst are respectively purified at a predetermined period of time.